1. Field of the Invention
Embodiments of the invention relate to an apparatus used for the delivery of chemical precursors, and more particularly, to an ampoule for containing chemical precursors.
2. Description of the Related Art
Integrated circuits have evolved into complex devices that include millions of transistors, capacitors, and resistors on a single chip. The evolution of chip design continually requires faster circuitry and greater circuit density demanding increasingly precise fabrication processes. The precision processing of substrates requires precise control of temperature, rate, and pressure in the delivery of fluids used during processing.
Chemical vapor deposition (CVD) and atomic layer deposition (ALD) are vapor deposition processes are used to form or deposit various materials on a substrate. In general, CVD and ALD processes involve the delivery of gaseous reactants to the substrate surface where a chemical reaction takes place under temperature and pressure conditions favorable to the thermodynamics of the reaction. The type and composition of the layers that may be formed using a CVD process or an ALD process are limited by the ability to deliver a chemical reactant or precursor to the substrate surface. Various liquid precursors have been successfully used during CVD and ALD applications by delivering the liquid precursors within a carrier gas.
A carrier gas is in some cases passed through a heated vessel or canister, such as an ampoule or bubbler, which contains a volatile liquid precursor under conditions conducive to vaporize the precursor. In other cases, a carrier gas is passed through a heated vessel containing a solid precursor under conditions conducive to sublime the solid precursor. The sublimation process is typically performed in a vessel loaded or filled with a solid precursor, and the vessel walls are heated to sublime the solid precursor material while producing a gaseous precursor. In either case, the carrier gas combines with the vaporized precursor to form a process gas which is drawn from the vessel via dedicated conduits or gas lines to a reaction chamber.
A vapor deposition process that utilizes a solid precursor may suffer several problems. While a solid precursor should be provided enough heated to be sublimed into a gaseous state, the solid precursor may decompose if exposed to too much heat. Metal-organic solid precursors, which are usually very expensive, are especially susceptible to thermal decomposition and generally need to be maintained within narrow temperature and pressure ranges during a sublimation process. Once decomposed, solid precursors may contaminate the remaining precursor in the vessel, the delivery system of conduits and valves, the processing chamber, as well as the substrate. Furthermore, overheating a solid precursor may provide too high of a precursor concentration within the process gas, which may lead to wasted precursor that is never used or condensation of the precursor within the delivery lines or on the substrate.
Alternatively, the solid precursor may not sublime if exposed to too little heat. As the carrier gas is flowed through the vessel and impacts the solid precursor, particulates from the solid precursor may become entrained in the carrier gas and transferred into the process chamber. These undesired solid or liquid particulates may become a source of contamination for the delivery system, processing chamber, or substrate. The problem of particulate contamination has been addressed in the art by including a liquid carrier material mixed with a solid precursor. However, the mixture of the liquid carrier material and the solid precursor may only be conducive within limited temperature and pressure ranges since the liquid carrier material may be evaporated and become a contaminant within the delivery system, processing chamber, or on the substrate.
Therefore, there is a need for an improved apparatus for providing a process gas derived from a solid precursor to a processing chamber.